Small-scale vortex over the tropical Atlantic Ocean

September 25th, 2010 |
GOES-13 0.63 µm visible image (courtesy of Tony Cristaldi, NWS Melbourne FL)

GOES-13 0.63 µm visible image (courtesy of Tony Cristaldi, NWS Melbourne FL)

Tony Cristaldi (National Weather Service Forecast Office in Melbourne, Florida) sent the following email (with the attached GOES-13 visible image shown above):

There is a very small cyclonic swirl to the southwest of Lisa near 12N 35W, that has been firing off central convection since Friday afternoon. Now, one wouldn’t expect a feature of this magnitude to be carried operationally as a TC, since these features are often times transient, being very vulnerable to even modest amounts of low level deformation and mid of upper level wind shear. Nevertheless, since it has persisted since early this morning, I thought I’d pose a couple questions: 1) Looking at visible imagery, does it appear that convection is persisting due to a warm core TC process (CISK) on a very small scale, or a more traditional low level mesoscale convective process? 2) Would you call this feature a “micro-midget?”

At his request, we created a 2-day animation covering the period 24-25 September 2010, using GOES-13 0.63 µm visible images during the daytime and GOES-13 3.9 µm shortwave IR images at night (below). The low-level “swirl” appeared to be propagating southeastward, and it was indeed firing off some impressive convective bursts (with a few cloud top IR brightness temperature values as cold as -70º C).

GOES-13 0.63 µm visible images (daytime) and 3.9 µm shortwave IR images (night-time)

GOES-13 0.63 µm visible images (daytime) and 3.9 µm shortwave IR images (night-time)

Not quite sure exactly what to call it…but thanks to Tony for bringing this interesting feature to our attention!

Strong mid-latitude cyclone over Lake Superior

September 24th, 2010 |
GOES-13 6.5 µm water vapor channel imagery

GOES-13 6.5 µm water vapor channel imagery

A strong mid-latitude cyclone intensified over the Lake Superior region on 24 September 2010. This storm produced wind gusts as high as 42 knots (48 mph), which caused some tree damage and some minor coastal flooding in parts of the Upper Peninsula of Michigan.

AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above) showed the evolution of the cyclone as it intensified during the day.

Greater detail could be seen in 1-km resolution MODIS 6.7 µm water vapor channel images at 16:21 UTC and 18:24 UTC (below).

MODIS 6.7 µm water vapor channel images

MODIS 6.7 µm water vapor channel images

“Anvil plumes” associated with severe convection in NE and SD

September 22nd, 2010 |
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

Clusters of severe thunderstorms developed across parts of northeastern Nebraska and southeastern South Dakota ahead of a warm frontal boundary that was advancing northward across the region on 22 September 2010. These severe thunderstorms produced a number of reports of large hail and damaging winds. AWIPS images of GOES-13 10.7 µm IR data (above) showed that cloud top IR brightness temperatures were as cold as around -70º C (dark black enhancement) at times.

The corresponding GOES-13 3.9 µm shortwave IR images (below) revealed that a few interesting “darker plumes” developed on the cloud tops of some of the southernmost storms — this darker appearance was a signature of smaller ice crystal particles that were being ejected above the anvil top by some of the stronger thunderstorm updrafts. These smaller ice crystals were better reflectors of incident solar radiation, making them show up as warmer (darker) features on the shortwave IR images.

GOES-13 3.9 µm shortwave IR images

GOES-13 3.9 µm shortwave IR images

These darker anvil top plumes were also very evident at 16:33 UTC on 1-km resolution MODIS 3.7 µm shortwave IR imagery (below).

MODIS 3.7 µm shortwave IR image

MODIS 3.7 µm shortwave IR image

A closer view using 1-km resolution POES AVHRR 10.8 µm IR imagery at 18:56 UTC (below) displayed a well-defined “enhanced-v” signature in southeastern South Dakota (with the coldest cloud top IR brightness temperature value of -82º C, violet color enhancement) — and a large number of hail reports associated with this storm as it tracked through the area, including a report of 3.5 inch diameter hail near Vermillion, South Dakota.

POES AVHRR 10.8 µm IR image (with hail reports)

POES AVHRR 10.8 µm IR image (with hail reports)

GOES-15 Super Rapid Scan Operations (SRSO) 1-minute interval images over the Upper Midwest

September 21st, 2010 |

GOES-15 1-minute interval (SRSO) 0.63 µm visible channel images

GOES-15 1-minute interval (SRSO) 0.63 µm visible channel images

21 September 2010 was the final day of the GOES-15 Post Launch Science Test — and the satellite was placed into Super Rapid Scan Operations (SRSO) mode to provide images as frequently as every 1 minute over the Upper Midwest region. A set of SRSO 0.63 µm visible images  (above) showed the evolution of clusters of severe thunderstorms with overshooting tops that were producing large hail and damaging winds across parts of Iowa, northern Illinois, and southern Wisconsin during the 20-22 UTC time frame (SPC Storm Reports).

The full set of 1-minute interval SRSO 0.63 µm visible, 10.7 µm IR, and 6.5 µm water vapor images (from 12:45 UTC to 23:45 UTC on 21 September) are available as either QuickTime movies or as Animated GIF files (below).

GOES-15 1-minute interval (SRSO) 0.63 µm visible images

GOES-15 1-minute interval (SRSO) 0.63 µm visible images

GOES-15 1-minute interval (SRSO) 10.7 µm IR images

GOES-15 1-minute interval (SRSO) 10.7 µm IR images

GOES-15 1-minute interval (SRSO) 6.5 µm water vapor images

GOES-15 1-minute interval (SRSO) 6.5 µm water vapor images

In addition to the severe convection, there were a number of small agricultural fires burning  across parts of northern Arkansas into the Boothill of Missouri region and extreme southern Illinois. A comparison of GOES-15 3.9 µm shortwave IR images at 1-minute intervals (below; top panels) vs the “normal” operational 15-minute interval (below; bottom panels) demonstrates the improved ability to monitor the temporal variability of such small and often short-lived fires (which were denoted by the hotter yellow to red pixels).

GOES-15 3.9 µm shortwave IR images: 1-minute interval (top) vs 15-minute interval (bottom)

GOES-15 3.9 µm shortwave IR images: 1-minute interval (top) vs 15-minute interval (bottom)